In a classical method of manufacture of a tire, the side walls are formed already on the carcass building drum. Before or after placing the core and the core profiles, the laterally protruding rubber layers are bent back toward the center and then form the starter element of the first build-up stage. In this step, the side wall rubber is already applied or “built in”.
With the subsequent shaping of the cylindrically-shaped starter element to a torus-shaped tire body, it must be considered that the geometry of the carcass can change because of expansion during shaping and also the volumes of the rubber layers, that is, therefore also those of the side wall rubber parts can shift so that already in advance an adjustment with respect thereto for compensation must be undertaken with the adjustment being determined empirically. After placing the belt ply packet, the vulcanization takes place during which a further displacement can be observed which likewise must be compensated by an advance adaptation of the entire manufacturing process. During the vulcanization, the completed starter element is subjected to an internal pressure via a bellows and is placed under increased temperature and then receives its so-called “residual rise”, that is, an additional expansion to adapt to the vulcanization form. Such a compensation has associated with it the disadvantages that in those regions, which are subjected especially to the expansion, such as, for example, the sides, a precise metering of the rubber volume and an exact shaping are difficult.
The term “belt ply packet” is a conventional technical term in tire manufacture which does not only include the belt, that is, the belt layers per se, but also the additional components above the belt, which complete the tire starter element, namely, the tread and, if required, belt layers which may be present, inserts and tread strip substrate. This results from the manufacturing procedure, which is conventional in the classical two-step process, wherein these components are assembled to an annular-shaped packet on the belt build-up drum. The carcass starter element (the carcass packet), which is manufactured on a separate carcass build-up drum, is then pressed into the annular-shaped packet while expanding (shaping).
In retreading, methods are known wherein, after a corresponding preparation and brushing of the surfaces of the old tire (that is, the already contoured tire) via cold processing and heat processing, a new side wall rubber can also be applied. In contrast to the application of the tread (which can be placed on an approximately cylindrical surface), not only the disadvantage exists in the side walls placed in strip form, that a straight strip of side wall rubber has to be applied to an intensely convex side surface (arcuate outwardly) but the problem also exists that the side wall rubber strip is formed transversely to its longitudinal direction to a disc-shaped form which, in the strip material, causes intense deformations or expansions because of the different radii which then arise.
For this too, in the sense of an advance compensation, the side wall rubber strip has to be configured with a trapezoidally-shaped or triangular cross section so that, after the corresponding expansions, an almost equal strip thickness still remains on the side wall.
An additional problem is that the side wall strip, which is applied on a circular annular surface arched outwardly, must be cut to length after placement which leads to the situation that the radially outward regions, which are subjected to a significantly greater expansion than the radially inner regions, retract from the cut location whereby an approximately triangular or trapezoidal opening of the strip would result if the cut were not set correspondingly inclined or overlapping.
Each overlapping effects, however, an additional thickening of the side wall at only one location which is unwanted because of optical reasons but also because of the imbalance. As a rule, the excess must therefore be shaved which, in turn, disturbingly affects the production process, that is, the process of retreading.
A solution to this problem is disclosed in German utility model registration DE 296 12 955 U1 which discloses an arrangement with which the side walls can be injected, that is, extruded via extruder shoes which are especially formed and lie on the prepared surfaces. A solution of this kind ensures, inter alia, a uniform application of rubber via the special configuration and the pressing flat of the sides of the carcass but includes the disadvantage that, on the one hand, for each tire size, a special shoe must be provided and, on the other hand, a variable configuration of the thickness cannot be carried out only by influencing the extruder nozzle or the speed profile or even a change of the rubber mixture above the tire elevation. When retreading, pressing the sides flat has the additional disadvantage that, because of interruptions in stiffness in the sides already present in the tire (that is, such as by overlappings from the original manufacturing process), the applied layer thickness can be influenced.
U.S. Pat. No. 4,963,207 discloses a method for manufacturing new tires wherein all rubber parts of the tire are applied with the aid of one or several volumetric extruders movable in several axes. For this purpose, a tire build-up drum is used which is essentially already adapted to the later tire contour and is configured with a form of the side walls, treads, bead regions, et cetera, which substantially approaches a finished tire.
This rotating build-up drum is, as a rule, made of aluminum and all rubber parts, that is, treads, side walls, beads, et cetera, are sprayed thereon. Thereafter, the drum functions as a holding element to stabilize the form of the tire, which has not yet vulcanized, during the transfer to and in the vulcanization press. This has the consequence that the aluminum drum with the rubber is taken out of the wrapping position and is placed in an especially adapted vulcanization press in which a further outer form encloses the build-up drum and the tire and completely vulcanizes the tire.
With this method, the disadvantage is present that, for each vulcanization operation, the tire build-up drum must be transported and a precise and adjustable additional outer form (adapted to the production process) must be produced and the aluminum core, that is, the build-up drum, must be so configured that it can again be removed from the tire after the vulcanization and can again be built up within the wrapper station so that the advantage of the very variable and precise application of the rubber to all tire regions must be accepted with serious changes with respect to the classical manufacturing and vulcanization process.